Method for the manufacture of laminated electromagnetic cores



Nov. 10, 1970 -r ETAL 3,538,601

METHOD FOR THE MANUFACTURE OF LAMINATED ELECTROMAGNET CORES Filed May20, 1968 g I INVENTORS Patrick J-M. NEROT Claude P. VINOT United StatesPatent Int. Cl. rioir 7/06 U.S. Cl. 29-609 Claims ABSTRACT OF THEDISCLOSURE A method for the manufacture of an electromagnet core made ofa movable and of a stationary part WhlCh comprises assembling punchedlaminations into two stacks to form the said parts, each defining apolar surface and truing only one of said polar surfaces, by grinding,the other polar surface remaining rough.

An electromagnet core formed of a movable and of a stationary part andmade of laminations stacked into the said parts, each part defining apolar surface. One of the polar surfaces is a polished surface whereasthe other polar surface is defined by rough edges of the correspondinglaminations.

-The present invention relates to a method for the manufacture oflaminated electromagnet cores and cores so obtained.

More specifically, the present invention relates to a very simple methodfor manufacturing stationary or movable laminated cores usually used inalternating current ,electromagnets. These cores are made in magneticlaminations punched in the form of an E or an U, the said laminationsbeing thereafter assembled in generally riveted stacks. In many devices,such as relays or contactor,.one of these stacks forms the stationaryportion and carries the magnetic coil that creates the magnetic flux onone of its branches whereas the other portion, called the armature, ismovable in translation or in rotation of a relatively small angle.

A method for the manufacture of an electromagnet will be found, by wayof example, in U.S. Pat. No. 2,997,- 633, issued Aug. 22, 1961. Such anelectromagnet is capable of resisting a very high number of operationswithout decreasing the quality of the magnetic circuit with regard tothe ill effects of the residual magnetism.

One object of the manufacturing method of the invention lies in that itmakes it possible to obtain still better results with simpler, andconsequently, more economical means. It relates to a two-partelectromagnet of which one part is movable in relation to the other,that obviates the sticking effect of the polar surfaces and with a veryhigh manoeuvring possibility without deterioration of the said surfaces.It is applicable to all shapes of electromagnet cores but it isparticularly efiicient for a magnetic core made of two branches such asthose made with U-shaped laminations and provided with an antiresidual 4air gap incorporated in the branches. This type of electromagnet isdescribed and illustrated in U.S. Pat. N0. 1,518,020, issued Dec. 2,1924.

When the antiresidual air gap is obtained by a narrow space resultingfrom an interruption in the metal of the core branches themselves andnot by the polar surfaces that separate the stationary and movableparts, it is sure that the antiresidual air gap will remain constanteven after a very large number of operations as it will not be alteredby wear or by the meeting surfaces of the parts being pushed back. It isconsequently not necessary in such a case to harden the said surfaces bya chemical treatment. But, as has been observed in the prior technique,it is advantageous to provide the meeting surfaces of the electromagnetwith a fine oil film which, on the one hand, gives protection againstcorrosion and, on the other hand, absorbs the meeting shock. Thisgreasing method by an oil reserve located between the laminations andthat slowly seeps onto the polar surface is already known by itself andalready provides a very important improvement in the quality ofelectromagnetic subjected to armature shocks repeated several millionsof times.

The oil reserve between the laminations may be used as well as withE-shaped three-branch cores or U-shaped two-branch cores. In each case,there will be two cooperating polar surfaces narrowly joined since, ifthe core is U-shaped, there must be an incorporated air gap.

In known manner, these joined surfaces are obtained by truing up thestack of assembled laminations by grinding. The coexistence of thesemeans: the oil film on the polar meeting surfaces and the same surfacesbeing trued up by grinding has drawbacks. On the one hand, duringrepeated closures of the armature, the oil film bursts and splashes onthe external parts. On the other hand, the flat polished surfaces have atendency to stick to one another and prevent the reopening of themagnetic circuit. To obviate this, truing by grinding of the two partsof the core could obviously be totally omitted but the magnetic circuitwould then vibrate and make a great noise when excited.

In a magnetic core of a laminated electromagnet comprising an oilreserve supplying an oil film on the polar surfaces, a surprising effecthas been noted that if, according to the invention, all of the polarsurfaces of one part of the core are trued up by grinding whereas thecooperating surface of the other part is only equalized by ramming butnot trued up, the sticking effect of the said surfaces is avoidedsimultaneously with obtaining a much greater number of operations thanusually obtained with industrial electromagnets.

By way of example, one embodiment of a method for the manufacture of amagnetic core according to the invention will now be given withreference to drawings, such embodiment is limited however to the onlyfeatures of the method, it being understood that the construction I oflaminated cores is well known in itself.

spread over the laminations during punching. Then the laminations aredegreased by immersion in a bath of liquid trichlorethylene at atemperature of 87 C., the immersion period being'about 20 minutes toobtain a weight of oil of 0.2 mmg./cm. This figure is suitable for asmall magnetic core of 76 g. such as used in relays. For more involvedmagnetic cores, the amount of oil may attain 0.5 mmg. per cm. theimmersion period being then reduced. In every case, experimentation mustbe made and the amount of oil needed may vary from 0.1 to 0.5 mmg. percm. One of the stacks of laminations, for instance that whichconstitutes the armature 1 of the electromagnet, may thereafter beassembled by any convenient means such as rivets 2. It is thereaftertrued up by grinding to obtain perfectly fiat polar surfaces 3. The

other stack of laminations, corresponding in this instance to thestationary part 4, is placed in a gig and also assembled. The polarsurface 5 of the latter stack is thus, constituted by the rough edges ofthe punched laminations without any particular hardening treatment.However, as the punched laminations are removed from the machine, theyare progressively picked up by stringing them in such a way that theymay be assembled parallel with an in the same direction as that of thework of the punching tool. It will be observed also that a certainhardness is already obtained by the cold hammering of the metal in thework of the press tool. This second stack of laminations remaining inits gig is then rammed by a force directed in the plane of thelaminations and against the polar surfaces. For this purpose, it is onlysufficient to'give these surfaces a simple press blow. The two stacks oflaminations are then joined and assembled with the other parts of theelectromagnet.

With a two-branch circuit constructed according to the above-describedmethod, it has been possible to obtain a satisfactory working duringforty million operations. The method is extremely economical since itrequires no special chemical or thermal treatment and that it even omitsone of the usual truing operations.

The very interesting technical result obtained may be explained asfollows: the polar surfaces 3 and 5 movable against one another are ofdifferent physical nature. On the one hand, a surface 3 polished by thework of the millstone, on the other hand, an irregular surface 5 formedof very small grooves 6 as illustrated in FIG. 2. Indeed, during thepunching operation of the laminations, there is produced along thepunched contour a small round on one side and a small burr on the otherside rather than two sharp edges. Thus, the parallel assembly of thepunched laminations in the same working direction gives, on the edge ofthe stack of laminations, a series of narrow parallel surfaces separatedby minute edgy groove 6; besides, these surfaces have been subjected toa certain hardening inherent to the cold working of the metal. Thegroove '6 thus formed and that would disappear if they were trued up bygrinding will thus serve to hold into position the oil film that comesfrom the reserve between the laminations. Furthermore, the cooperatingpolar surfaces 3 and 5 may no longer adhere as would two polishedsurfaces under atmospheric pressure. Finally, the voids corresponding tothe grooves fin rea e ta c ..,th ma neti c rcu tthus proving theantiresidual effect.

It is clear that the scope of the invention is not limited toelectromagnet parts as described above but that it also relates to anyother assembly of magnetic laminations of an alternating currentelectric apparatus.

We claim:

1. A method of manufacturing a laminated electromagnet core comprising:punching metal laminations into a predetermined shape; spreading overthe surface of the laminations a predetermined amount of oil which isproportional to the size of the laminations; assembling said punchedlaminations in parallel relationship into stacks to constitute two coreportions defining rough polar surfaces while maintaining a commondirection for the mounting of the stacked laminations with regard to thepunching direction, truing up the rough polar surfaces of only one ofsaid stacks by grinding, aligning the laminations of the other stack byramming against its rough polar surface, and assembling said two coreportions to form an electromagnet core having cooperating polarsurfaces.

2. Amethod as defined in claim 1 including degreasing said laminations.

3. A method as defined in claim 2 wherein said degreasing includesimmersing said laminations in a bath of liquid trichlorethylene.

4. A method as defined in claim 1 wherein said predetermined amount ofoil spread over the surface is from 0.1 mmg./cm. to and including 0.5mmg./cm.

5. A method as defined in claim 1 including forming minute grooves onsaid polar surfaces when said laminations are assembled in parallelrelationship.

References Cited UNITED STATES PATENTS 1,834,898 12/1931 Boyajian 29-6092,541,502 2/1951 Cross et al. 29-609 X 2,997,633 ,8/1961 Ellis et a1.335-281 3,058,039 10/1962, Ray 335-281 X JOHN F. CAMPBELL, PrimaryExaminer C. E. HALL, Assistant Examiner US. 01. X.R. 29-602; 335-281;336-212, 234

